Problem: Some cars were parked in the grocery store parking lot. 4 more cars park at the grocery store. Now there are 12 cars in the parking lot. How many cars were parked at the grocery store at the beginning?
Solution: The number of cars parked at the store at the beginning is the difference of the number parked now and the number that came and parked earlier. The difference is $12 - 4$ cars. $12 - 4 = 8$ cars.